1. Technical Field
Example embodiments of the present invention relate to a reference voltage generator, and more specifically to a bandgap reference voltage generator insensitive to changes of process, voltage, and temperature.
2. Related Art
Almost of analog, high-frequency, and digital circuits made in a chip form needs stable and precise bias voltages in order to enhance operation efficiency.
However, a bias voltage provided from general bias circuits may not maintain a constant voltage according to changes of process, voltage, and temperature (PVT). In order to overcome the above problem, a bandgap reference voltage generator designed to be insensitive to changes of PVT is being used.
Usually, bandgap reference voltage generators may use voltage between a base and an emitter of bipolar transistor, since temperature characteristics of the voltage between a base and an emitter of bipolar junction transistor (BJT) is more excellent than those of metal oxide semiconductor (MOS) transistor such as threshold voltage and mobility.
Thus, performance of bandgap reference voltage generator using BJT is limited by non-linearity of the voltage between base and emitter of the BJT, and thereby various curvature compensation techniques have been proposed in order to enhance performances of bandgap reference voltage generators using BJT. Most of the curvature compensation techniques focus upon attenuating non-linearity of the voltage between base and emitter.
Meanwhile, even though temperature characteristics of the BJT are more excellent than those of MOS transistor, characteristics according to changes of process and power supply voltage may not be guaranteed.
For example, a Korean published application 10-2010-0026389 filed by the present applicant disclosed a bandgap reference voltage generator having an excellent temperature coefficients 9 ppm/ in the case of general Typical-Typical (TT) process condition. However, the above bandgap reference voltage generator has temperature coefficients 48.3 ppm/ and 138.8 ppm/ respectively for Fast-Fast (FF) process condition and Slow-Slow (SS) process condition. That is, the bandgap reference voltage generator disclosed in the above published application KR 10-2010-0026839 has a problem that temperature compensation according to changes of process is not performed appropriately in process conditions except the TT process condition, and so the above bandgap reference voltage generator has similar performance in process conditions except the TT process condition.
In order to resolve the above problem, a method of preventing performance degradation by control values of resistors constituting bandgap reference voltage generator has been proposed, since changes of characteristics according to changes of process and power supply voltage are most severe in resistors. However, the above method needs a plurality of resistors to compensate resistance value which varies more than 30 percent according to process and a plurality of fuse circuits connected to each of resistors in parallel. Therefore, large area on a chip is needed to implement the above method, and there are difficulties to control the resistance values minutely and limits in obtaining optimized performances.